1. Field of the Invention
The present invention relates to an image reading apparatus which receives light reflected from, or passing through, an original, whereby it reads the image printed on the original and supplies image signals representing the image to an external apparatus such as a computer.
2. Description of the Related Art
As a result of the development, and now widespread availability, of personal computers able to process image data, a variety of image reading apparatuses has been developed, which are designed to input image data into such computers, and are now being used in increasing numbers. An example of such image reading apparatuses is that disclosed in U.S. Pat. No. 4,623,937, granted to J. Watanabe. This apparatus receives the light irradiated from a light source onto an original and reflected therefrom, and converts this reflected light into electric signals representing the image printed on the original. Also available is an image reading apparatus which receives and converts the light passing through an original into electric signals representing the image printed on the original.
Since, however, none of the conventional image reading apparatuses is able to read images by using either the light reflected from an original or else the light passing through it, i.e. they are confined to one or other of these modes, demand has therefore arisen for an image reading apparatus capable of operating in both the above-described modes.
When the original is a sheet of paper, the image printed thereon is normally read by way of the light reflected therefrom, while when it is a transparent film or sheet of OHP paper, the image thereon is read by way of the light passing through the original. While a positive image printed on a transparent film can also be read by way of the light reflected from the original, the image thus-obtained tends to have low resolution. This is because the light applied to the original cover (i.e., having a white surface) diffuses as it passes through the original cover, with the result that the image read on the basis of the light reflected from the film, in particular, fine detail, will inevitably be blurred. Thus, the positive image printed on a transparent film should ideally be read by way of the light passing through the film, as opposed to the light reflected therefrom.
As has been pointed out, no single conventional image reading apparatus can read an image by using either the light reflected from an original or else the light passing through it. Thus, two different image reading apparatuses must be used if it is required that images be read by way of light reflected from originals, as well as by light passing through originals.